Oil pumps are used in vehicle engines to circulate engine oil inside the engines. The oil pumps are connected to and driven by an external drive source such as a crankshaft. One of such oil pumps is disclosed, for example, in Japanese Patent (JP) No. 4160963. The oil pump disclosed in JP 4160963 is shown in FIGS. 11 and 12 hereof.
As shown in FIG. 11, a conventional oil pump 210 includes a rotating shaft 211, an inner rotor 212 attached to the rotating shaft 211, an outer rotor 213 surrounding the inner rotor 212 and rotated by the inner rotor 212, and a housing 220 within which the rotating shaft 211, the inner rotor 212 and the outer rotor 213 are housed.
FIG. 12 is a view illustrating the housing shown in FIG. 11 with the rotating shaft, the inner rotor and the outer rotor removed. As shown in FIG. 12, the housing 220 includes a suction port 231 from which oil is sucked in, a discharge port 240 from which the oil is discharged, and a partitioning section 233 formed to partition the suction port 231 and the discharge port 240. The discharge port 240 has discharge groove portions 241, 242 formed at a part thereof so as to introduce the oil from the partitioning section 233. The discharge groove portions 241, 242 are formed to become gradually deeper along a direction in which the oil flows.
Referring back to FIG. 11, when an engine is operated, a crankshaft is rotated, and the rotating shaft 211 connected to the crankshaft is caused to rotate. As the rotating shaft 211 rotates, the inner rotor 212 is thereby caused to rotate. Then, the outer rotor 213 partially engaged with the inner rotor 212 is caused to rotate.
At the suction port 231, oil is filled in a space Sp formed by the inner rotor 212 and the outer rotor 213. In accordance with the rotation of the inner rotor 212 and the outer rotor 213, the space Sp moves over the partitioning section 233, and then reaches the discharge port 240. The oil carried to the discharge port 240 is discharged from the discharge port 240 to the outside of the oil pump 210.
In the oil pump 210, the discharge groove portions 241, 242 are formed adjacent to the partitioning section 233. With the discharge groove portions 241, 242 formed to become gradually deeper, flow passage area of oil becomes gradually larger. By making the flow passage area gradually larger, a sudden change of oil flow rate is suppressed. As a result, it is possible to prevent occurrence of cavitation in the housing and prolong a lifetime of the oil pump 210.
In the conventional oil pump, however, when the space Sp reaches an end of the partitioning section 233, the flow passage area increases at this position. The sudden increase in the flow passage area at this position would cause a cavitation in the housing. There is still room for further improvement in this regard.